Circuit arrangement for generating high voltage pulses

ABSTRACT

A circuit arrangement for generating high voltage pulses from DC voltage. The circuit includes a transformer comprising at least two primary windings and secondary windings, in which the primary windings are serial connected with at least one diode, a switching circuit and a voltage source. A first capacitor is connected in parallel with the first primary winding and diode, and in series with the secondary primary winding. The switching circuit is formed from the emitter-collector-section of a switching transistor. The output of a transistor amplifier is connected to the base of the switching transistor. The input of the transistor amplifier is coupled with the output of a control circuit. Two serial connected resistors are inserted between the input of the transistor amplifier and the output of the control circuit. The emitter-collector-section of a first transistor is connected to the common terminal of both the resistors. A voltage divider is connected to the base of the first transistor. The leg of the voltage divider on the collector side of the first transistor includes two serial connected resistors. A second capacitor is connected between (a) the point between the two serial connected resistors in the leg of the voltage divider on the collector side of the first transistor, and the common terminal of the primary winding of the transformer and of the switching transistor. A current sensing resistor is connected in series with the emitter-collector-circuit of the switching transistor.

TECHNICAL FIELD

The invention relates to a circuit arrangement for generating highvoltage pulses from DC voltage comprising a transformer, a secondarywinding and at least two primary windings of said transformer, saidprimary windings, at least one diode and a switching circuit are serialconnected; said series circuit is connected to a voltage source, acapacitor is connected to the common terminal of said voltage source andof said primary windings, further said switching circuit is formed fromthe emitter-collector-section of a switching transistor, on the base ofsaid switching transistor the output of a transistor amplifier isconnected and the input of said transistor amplifier is coupled with theoutput of a control circuit.

The generating of pulses, especially of high voltage pulses isfrequently needed in the electrotechnics and electronics. This demandoccurs very often in the field of the vehicle electrics, where the highvoltage sparks for the ignition of internal combustion motors aregenerated by high voltage pulses. Such high voltage pulses are used tothe ignition of flash tubes too, which are applied not only in thephototechnics, but also in traffic control systems and many othertechnical fields. We described the invention in relation with ignitionsystems of internal combustion motors, nevertheless the invention is notlimited to this technical field.

BACKGROUND ART

Electronic ignition systems of internal combustion motors are commonlyused, which systems may be divided into two groups. In the first groupthere are the so-called thyristor or capacitive ignition systems; insuch a system a capacitor will be charged and the stored energy of thiscapacitor will be switched on the primary winding of the high voltagetransformer by means of a thyristor at the instant of the ignition. Theadvantage of such systems is that the contact breaker, which controlsthe instant of the ignition, switches very small current only, thereforethe lifetime of the contact breaker increases. The drawback of suchsystems is however that an inverter is needed to charge the capacitor,which owing to its structure needs many components, is expensive, andduring the short time between two pulses only a limited amount of energycan be stored in the capacitor at acceptable cost.

To the second group of electronic ignition systems belong the so-calledtransistor ignition systems; in such a system not a contact breaker, buta switching transistor circuit is serial connected to the primarywinding of a conventional ignition coil. In such a system the contactbreaker is disburdened too, since it generates a control pulse of verysmall current only and a switching transistor is used to interrupt thehigh current of the primary winding. The advantages of such a system isthe disburdening of the contact breaker, and that higher current pulsescan be interrupted in the primary winding of the ignition coil.

It is well known that the quality of the combustion in an internalcombustion motor as well as the efficiency of the motor can be improvedin that way that the ignition of the fuel will be effected moreperfectly, and this is possible by increasing the energy of the ignitionspark.

As we mentioned, in capacitive ignition systems the increasing of theenergy of the spark is limited by the complexity and costs of thesystem. The energy converting efficiency of transistor ignition systemsis relatively low. The energy of the high voltage pulse as well as thatof the spark changes significantly with the change of the supplyvoltage, and this hampers especially the cold starting of internalcombustion motors of vehicles. As it is well known, at cold starting thestarting electric motor reduces the voltage of the cold start battery tosuch an extent that this reduced battery voltage is frequently notenough to generate the ignition spark.

It is the aim of the Hungarian Pat. No. 186,116. "Circuit arrangementfor generating high voltage pulses" to eliminate these drawbacks, inwhich the primary winding of the high voltage transformer is dividedinto two winding parts. In this known circuit one of the primarywindings of the transformer as well as a switching circuit and acapacitor form together a loop circuit. Both primary windings are serialconnected and over a diode they are connected to a voltage source. Theoperation principle of this circuit is that at the instant of switchingon the switching transistor forming a switching circuit the storedenergy of the capacitor drives current through one of the primarywindings of the transformer, which current adds itself to the currentflowing from the voltage source and by this way a significantly highercurrent pulse can be generated through the primary winding.

It is the advantage of this circuit that at the interrupting of thecurrent flowing through the primary winding, that is when the switchingtransistor switches off, the voltage arising in the other primarywinding with opposite polarity and charges the capacitor. In this waythis is an energy recovery circuit, since the induced voltage arising atthe interruption of the current charges over the energy stored in thetransformer into the capacitor. In this way this is an energy recoverycircuit. Although this circuit worked well in the practice, the windingused to energy recovery does not work at generating the spark.

In the circuit arrangements described above theoreticallyelectromechanical switching devices could also be used as switchingcircuits, yet these have so many drawbacks that in electronic ignitionsystems they are used at most as control switches. To interrupt the highcurrent flowing through the primary winding of the transformer highpower switching transistors come above all into consideration. I haveused such a transistor in the ignition system according to my abovementioned Hungarian Pat. No. 186,116. In this known circuit theswitching transistor is actuated by a transistor amplifier, which iscontrolled by a control circuit. A negative feedback circuit is appliedcomprising a voltage dependent resistor so that lest the changing, firstof all the reduction of the supply voltage may significantly reduce theenergy of the pulse. This voltage dependent resistor - taking intoconsideration the low supply voltage, the needed characteristic and thevalue of the resistor - should be an incandescent lamp, yet thedimensions, lifetime and reliability of which are disadvantageouscompared to other components, and this is why the practicalapplicability of this circuit arrangement is limited.

The invention has for its object to provide a circuit arrangementdescribed in the opening paragraph, which should combine the advantagesof both the capacitive and the transistor ignition systems; moreover thestored magnetic energy should be recoverable with the best possibleefficiency and by this way the efficiency of the generating the highvoltage pulse should be improved. Another aim of the invention was toform such a switching circuit, by means of which the energy of the highvoltage impulse could be kept constant under a supply voltage changingwithin broad limits, what would be very advantageous especially to coldstarting of internal combustion motors of vehicles.

DISCLOSURE OF THE INVENTION

I achieved this object by means of the circuit arrangement of the kindmentioned in the opening paragraph in that the input of a transistoramplifier is the base of a second transistor, between said input and theoutput of a control circuit two serial connected resistors are inserted,to the common terminal of both said resistors theemitter--collector-section of a first transistor is connected, to thebase of the first transistor a voltage divider is connected, the branchof which standing on the collector side is divided and connected to avoltage source between the dividing point of said branch and the commonterminal of a primary winding of a transformer and of a switchingtransistor a capacitor is inserted, a resistor of said voltage dividerinserted on the emitter side is connected to a current control resistorwhich is in series with the emitter-collector-circuit of said switchingtransistor.

The advantage of this circuit arrangement is that by means of theapplied double feedback very steep switching of the switching transistorcan be achieved and in the same time the energy of the generated pulsekeeps practically constant even by a reduction of the voltage of thevoltage source by over 50%.

In the circuit arrangement according to the invention in a controlcircuit a series circuit comprising a pair of actuating contacts, aresistor and an induction coil is connected to said voltage source, thebase-emitter-section of a transistor is connected parallel to saidinduction coil having such a polarity that the voltage arising in saidinduction coil at the interruption of the current switches on saidtransistor, and the output of said control circuit is formed by thecollector of said transistor. The advantage of this circuit arrangementis that the structure of it is much more simple than that of the abovementioned Hungarian Pat. No. 186,116; in the same time the voltage pulsegenerated by the interruption of the current of the induction coil givesrise to a fast and definite switching.

It is further advantageous that between the base of said transistor andsaid induction coil a voltage divider is inserted. Expediently betweenthe collector of said transistor forming the output of said controlcircuit and said current control resistor a capacitor is inserted.

An advantageous embodiment of the invention aims to accelerate theswitching, in which a capacitor is connected parallel to said resistor,which is serial connected to the input of said transistor amplifier.

A further circuit arrangement according to the invention is alsoadvantageous to achieve the set aim, which comprises a transformer, asecondary winding and at least two primary windings of said transformer,said primary windings as well as at least one diode and a switchingcircuit are serial connected, said series circuit is connected to avoltage source, a capacitor is connected to the common terminal of saidvoltage source and of said primary windings, and which according to theinvention is characterized in that said diode is inserted between bothsaid primary windings, said capacitor is parallel connected to saidfirst primary winding attaching itself directly to said voltage sourceas well as to said diode connected serial to said first primary winding,and a further capacitor is parallel connected to said second primarywinding, as well as to said diode is connected serial to said secondprimary winding, and said diode is inserted in forward direction inrespect of the polarity of the voltage source. This last circuitarrangement has the advantage that at generating the pulse a significantpart of the energy supplied into the transformer can be recovered by theway that the magnetic energy stored in the iron core at the instant ofthe interrupting the current is charged over into the capacitor andstored in it, and afterwards this stored energy will be utilized to theenergy of the following pulse.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a circuit diagram of an energy recovery circuit of thetransformer according to the invention;

FIG. 2 is the equivalent circuit diagram of the circuit diagram of FIG.1 at the instant of the switching on;

FIG. 3 is an embodiment of the switching circuit according to theinvention;

FIG. 4 is the waveform of the current flowing through the switchingcircuit according to the invention; and

FIG. 5 shows the application of the switching circuit according to theinvention in the energy recovery circuit of the above mentionedHungarian patent HU-PS T/31.483.

BEST MODE OF CARRYING OUT THE INVENTION

In FIG. 1 the primary windings 2 and 3 of the transformer 1 of thecircuit according to the invention can be seen only, between which adiode 8 is inserted. The diode 8 is inserted in forward direction inrespect of the polarity of the voltage source 7. Capacitors 12 and 10are through the diode 8 parallel connected to the primary windings 2 and3 respectively. The terminals of the capacitor 12 are connected to thepositive pole of the voltage source 7 and to the cathode of the diode 8respectively. The terminals of the capacitor 10 are connected to theanode of the diode 8 and to the terminal of the primary winding 3standing toward the negative pole of the voltage source 7 respectively.The switching circuit 6 is inserted between the primary winding 3 andthe negative pole of the voltage source 7.

The function of the circuit shown in FIG. 1 is as follows.

At switching on the switching circuit 6 current begins to flow from thepositive pole through the primary windings 2, the diode 8, the primarywinding 3 and the switching circuit 6 into the negative pole of thevoltage source 7. Meanwhile magnetic energy is accumulated in theprimary windings 2 and 3. At switching off the switching circuit 6 thecurrent is interrupted through the primary windings 2 and 3 and avoltage jump of opposite polarity to the former voltage arises on theterminals of the primary windings 2 and 3. Accordingly the terminal ofthe primary winding 2 connected to the diode 8 will be of positivepolarity, and the terminal of the primary winding 3 connected to thecathode of the diode 8 will be of negative polarity. At this instant theprimary windings 2 and 3 can be considered as voltage sources and withthe said polarities the diode 8 is in conducting state. Thus the storedmagnetic energy of the primary winding 2 flows through the diode 8 intothe capacitor 12 and will be converted into electrostatic energy storedin the capacitor 12. Similarly the voltage jump arising in the primarywinding 3 charges the capacitor 10 through the diode 8. When themagnetic energy of the primary windings 2 and 3 has been fullyovercharged into the capacitors 12 and 10 respectively, the voltage onthe terminals of the primary windings 2 and 3 ceases and the diode 8switches off. The circuit rests in this condition.

At the instant of switching on again the voltages of the capacitors 12and 10 will add themselves to the voltage of the voltage source 7and--since the diode 8 is still in off state--the capacitor 12 will bedischarged through the primary winding 3 and the capacitor 10 throughthe primary winding 2 respectively. Taking into consideration that thecapacitors 12 and 10 can be charged up to a higher voltage, a highcurrent pulse arises through the primary windings 2 and 3. When thecharge of the capacitors has been used up, that is their voltages havedecreased, the diode 8 renders conducting and a current of the samedirection flows through the primary windings 2 and 3 and the diode 8between them from the voltage source 7. Under the influence of the highcurrent pulse flowing through the primary windings 2 and 3 a highvoltage pulse arises in the secondary winding of the high voltagetransformer not shown here. Of course the voltage source has to besuitable to lead through the high current pulse at the instant of thedischarge of the capacitors 10 and 12. This is easily possible in thecase of having a starter battery.

After the capacitors 12 and 10 have transmitted their energy to theprimary windings 3 and 2 respectively in form of said current pulses,they lose their charges, their voltages cease and afterwards the currentflowing from the voltage source 7 through the primary windings 2 and 3accumulates magnetic energy again in the iron core of the high voltagetransformer 1. Thereafter under the influence of the repeated switchingoff and on of the switching circuit 6 the process mentioned aboveoccures repeatedly and accordingly high voltage pulses arise.

In FIG. 3 the practically realized switching circuit according to theinvention is shown with the above mentioned circuit arrangement alsoaccording to the invention. In this circuit arrangement the transformer1 comprises two primary windings 2 and 3, between them a diode 8 isinserted with a polarity that in respect of the polarity of the voltagesource 7 the diode 8 is in forward direction. To the common terminalsbetween the diode 8 and the primary winding 2 or rather the primarywinding 3 capacitors are connected in such a way that capacitor 10 isconnected to the anode of the diode 8, the other terminal of which isconnected to the terminal of the primary winding 3 standing toward thenegative pole of the voltage source 7. To the cathode of the diode 8capacitor 12 is connected, the other terminal of which attaches itselfto the terminal of the primary winding 2 standing toward the positivepole of the voltage source 7. The transformer 1 comprises a secondarywinding 5 in which under the influence of the current pulse described inconnection with FIG. 1 and FIG. 2 respectively high voltage pulsearises.

In the switching circuit according to the invention shown in FIG. 3 theswitching circuit 6 is formed by a switching transistor 14. Theswitching transistor 14 is controlled by a control circuit 16 over aninserted transistor amplifier 15. In the transistor amplifier 15transistors 30 and 31 form together a two stage d.c. amplifier. In theexample shown here the transistor 30 is an npn transistor in commoncollector circuit and a resistor 32 is inserted in its emitter circuit.To the emitter of the transistor 30 the base of a transistor 31 isconnected, which is in common emitter circuit. The transistor 31 has aload resistance 33 in its collector circuit, the other terminal of whichis connected to the emitter of the switching transistor 14; which is inthis example in common collector circuit and is formed by a pnptransistor. The input 18 of the transistor amplifier 15 is the base ofthe transistor 30. A resistor 17 is serial connected to the input 18,which in an advantageous embodiment is divided into two parts, which areformed from the resistors 17a and 17b.

The output of a control circuit 16 is connected to the input 18 of thetransistor amplifier 15 over the resistors 17a and 17b. In the controlcircuit 16 a pair of actuating contacts 19, a resistor 20 and aninduction coil 21 are connected in series to the voltage source 7. Inapplications to internal combustion motors the pair of actuatingcontacts 19 is formed by the contact breaker of the motor. Thebase-emitter-circuit of a transistor 22 is parallel connected to theinduction coil 21. It may be practical to insert a voltage divider 23into the base circuit, which divides the voltage going to the base.

The function of the switching circuit 16 is--partly on the basis of thewaveform shown in FIG. 4--as follows.

At closing the pair of actuating contacts 19 a current begins to flowthrough the resistor 20 and the induction coil 21, and then the currentflowing through the induction coil 21 will be interrupted and a voltagewill be induced in it, the polarity of which is such that a positivevoltage jump will get to the emitter of the transistor 22 and a negativevoltage jump to the base of the same. It is to be noted that in theexample shown here the transistor 22 is of pnp type. Under the influenceof the voltage jump of the induction coil 21 the transistor 22 switcheson and from the voltage source 7 through the induction coil 21 and theemitter-collector-circuit of the transistor 22 a forward voltage gets tothe input 18 of the transistor amplifier 15. To the output of thetransistor amplifier 15 a capacitor 29 is connected--this we shallmention later again--, which is important in respect of the forming ofthe waveform on the input 18. When under the influence of the voltagepulse appearing on the induction coil 21 the transistor 22 switches on,then the current flowing through its emitter-collector-circuit is drivennot only by the voltage of the voltage source 7, but also by the voltagepulse connected serial to the former arising in the induction coil 21.

To the dividing point of the above mentioned divided resistor 17 betweenthe resistors 17a and 17b--which is principally the divided input pointof the input 18--the emitter-collector-circuit of a first transistor 24is parallel connected. By this way the input 18 of the transistoramplifier 15 as well as the switching transistor 14 is in off condition,when the first transistor 24 is in conducting condition. Between thecollector of the switching transistor 14 and the negative pole of thevoltage source 7--the latter is generally an earthed pole--a currentcontrol resistor 28 of very low value is inserted. The value of thiscurrent control resistor 28 is a few mOhms only, therefore practicallyit does not limit the current flowing through the switching transistor14 as well as the primary windings 2 and 3 of the transformer 1. To thebase of the above mentioned first transistor 24 a voltage divider isconnected, the resistor 27 of which laying on the emitter side connectedto the current control resistor 28. The resistor 25 of the same voltagedivider being on the collector side is connected to the positive pole ofthe voltage source 7 and is divided suitably in two resistors. Betweenthe dividing point of these two resistors and the common terminal of theswitching transistor 14 and of the transformer 1 a capacitor 26 isinserted. This capacitor 26 produces a voltage feedback to the base ofthe first transistor 24 and in the same time the voltage arising on thecurrent control resistor 28--which voltage is proportional to thecurrent--produces a current feedback to the base of the same firsttransistor 24.

The function of the circuit arrangement of FIG. 3 can be followed up onbasis of FIG. 4 too.

FIG. 4 shows the waveform of the current I flowing through the primarywindings 2 and 3 of the transformer 1, the switching transistor 14 andthe current control resistor 28 as the function of time t. At point Athe switching transistor 14 switches on and, as it has been described,the capacitors 10 and 12 connected serial to the voltage source 7 giverise to a high current pulse, which increases up to the point B. Atpoint B the charge of the capacitors 10 and 12 has been used up and thecurrent I decreases up to the point C. This current pulse induces a highvoltage pulse in the secondary winding of the transformer 1.

On the current control resistor 28 a voltage arises, which isproportional to the current I. This voltage adds itself to the voltagestored in the capacitor 29 and this results in that the transistor 30 aswell as the switching transistor 14 rests in on state further on, whenthe transistor 22 has been switched off.

This voltage arising on the current control resistor 28 controls thebase of the first transistor 24 too and in the vicinity of point B itmakes an effort to switch on the first transistor 24. Nevertheless themuch higher negative pulse arising on the capacitor 26 in the same timecounteracts it and keeps the transistor 24 in the vicinity of point Bstill safely in off state, therefore the switching off of the switchingtransistor 14 safely does not take place. With the knowledge of thevoltage divider of the transistor 24, of the capacitor 26, of thevoltage of the voltage source 7 and of the voltage drop arising on thecurrent control resistor 28 this function can easily be calculated.

In FIG. 4 after point B the discharge current of the capacitors 10 and12 decreases and at point C the current of the voltage source 7 onlyflows through the primary windings 2 and 3 and the diode 8, whichmeanwhile has been rendered conducting. From point C on the current Ibegins to increase with a slope defined by the inductivity of thetransformer 1. Reaching point D the voltage arising on the currentcontrol resistor 28 switches on the additional transistor 24 over theresistor 27. It is to be noted that the pulse of switching off polarityon the capacitor 26 is now no more present. At the instant of theswitching on of the transistor 24 the switching transistor 14 switchesoff abruptly and the interrupted current I induces a voltage of oppositepolarity in the primary windings 2 and 3, which charges up thecapacitors 10 and 12 again.

The temperature dependence of the transistor 24 is such that thetemperature dependent change of the forward voltage changes the positionof the point D on the diagram I. At lower temperature the point D movesinto the direction of the dash line in FIG. 4, i.e. the current I canincrease to a higher value. This again gives rise to the increase of themagnetic energy stored in the transformer 1, i.e. the high voltage pulseis practically of constant energy between broad limits in cold, at lowersupply voltage too. This is highly advantageous at the cold starting ofvehicles.

It may be advantageous to connect a capacitor 34 parallel to theresistor 17b, which speeds up the switching on the second transistor 30.

The switching circuit according to the invention and shown in FIG. 3 isapplicable to other pulse generating circuit too, the transformer 1 ofwhich is completed with an energy recovery circuit. An example of such acircuit arrangement is shown in FIG. 5.

The primary windings 2 and 3 of the transformer 1 as well as the diode 8are inserted serial into the emitter-collector-circuit of the switchingtransistor 14. Up to this point the switching arrangement corresponds tothat shown in FIG. 3. The difference is that the primary winding 3, theswitching transistor 14 and a capacitor 34 together form a loop circuit,as it is described in details in the above mentioned patentspecification HU-PS T/31.483. The function of the switching circuitaccording to the invention is the same in this case too as describedabove.

The above described circuit arrangement according to the invention hasbeen accomodated in the casing of a conventional ignition transformer.As the control circuit 16, the transistor amplifier 15 and in some casesthe switching transistor 14 are suitable to be integrated together ordeveloped as a hybrid circuit, so they can be easily accomodated in thecasing of a conventional ignition transformer together with the highvoltage transformer 1. By this way the complete circuit arrangementaccording to the invention can be directly exchanged for a conventionalignition coil used in vehicles today, no additional device, equipment orcasing is needed. This improves significantly the applicability of thecircuit arrangement according to the invention.

I claim:
 1. Circuit arrangement for generating high voltage pulses fromDC voltage comprising:a transformer including a secondary winding and atleast a first primary winding and a second primary winding; a rectifyingmeans connected between said first primary winding and said secondprimary winding; a first capacitor connected in parallel with said firstprimary winding and said rectifying means and in series with said secondprimary winding; switching means, comprising the emitter-collectorsection of a switching transistor connected in series with a currentsensing means, connected in series with said rectifying means and saidfirst and second primary windings to form a first series circuit; meansfor connecting said first series circuit to a voltage source; a controlmeans; an amplifying means; first connecting means for connecting anoutput of said control means to an input of said amplifying means;second connecting means for connecting an output of said amplifyingmeans to the base of said switching transistor; said first connectingmeans further comprising first and second resistors connected in series,the common terminal of said first and second resistors being connectedthrough the emitter-collector section of a first transistor to a firstterminal of said voltage source connecting means, and a voltage dividerconnected to the base of said first transistor, wherein said voltagedivider comprises a first leg including a third resistor and a secondleg including a fourth resistor and a fifth resistor connected inseries, said first leg connected to a terminal between said switchingtransistor and said current sensing means, said second leg connected toa second terminal of said voltage connecting means, and a terminalbetween said fourth and fifth resistors connected through a secondcapacitor to a terminal between said switching transistor and saidprimary windings.
 2. The circuit of claim 1, wherein said control meanscomprises:a pair of actuating contacts, a sixth resistor, and aninductor, all connected in series between said first and secondterminals of said voltage source connecting means; and a secondtransistor; wherein said inductor is connected between the base and theemitter of said transistor, the polarity of said second transistor isselected such that it turns on in response to the voltage induced in theinductor when the actuating contacts are opened, and the collector ofsaid second transistor connected to the output of the control means. 3.The circuit of claim 2, wherein said control means further includes avoltage divider between the base of said second transistor and saidinductor.
 4. The circuit of claim 1, wherein the output of the controlmeans is also connected through a third capacitor to said terminalbetween said switching transistor and said current sensing means.
 5. Thecircuit of claim 1, further comprising a capacitor connected between theinput to said amplifying means and said common terminal between saidfirst and second resistors.
 6. Circuit arrangements for generating highvoltage pulses from DC voltage comprising:a transformer including asecondary winding and at least a first primary winding and a secondprimary winding; a rectifying means connected in series between saidfirst primary winding and said second primary winding; a first capacitorconnected in parallel with said first primary winding and saidrectifying means and in series with said second primary winding; asecond capacitor connected in parallel with said second primary windingand said rectifying means and in series with said first primary winding;and switching means connected in series with said rectifying means andsaid first and second primary windings to form a series circuit; meansfor connecting said series circuit to a voltage source.